Recently, as the demand for portable electronic products such as notebooks, video cameras, mobile phones, and the like is rapidly increased, and the development of electric vehicles, energy storage batteries, robots, satellite, and the like is accelerated, high-performance secondary batteries capable of being repeatedly charged and discharged are being actively studied.
Currently commercialized secondary batteries include nickel cadmium batteries, nickel metal hydride batteries, nickel zinc batteries, lithium secondary batteries, and the like. Among these secondary batteries, since lithium secondary batteries have advantages of being freely charged and discharged due to almost no memory effect as compared with nickel-based batteries and having extremely low self-discharge rate and high energy density, lithium secondary batteries are spotlighted.
Such lithium secondary batteries mainly include a lithium-based oxide and a carbon material as a positive electrode active material and a negative electrode active material, respectively. Lithium secondary batteries include an electrode assembly, in which a positive electrode plate and a negative electrode plate respectively coated with a positive electrode active material and an negative electrode active material are arranged with a separator therebetween, and an exterior, that is, a battery case, in which the electrode assembly and an electrolyte are sealed and accommodated.
Generally, depending upon shapes of exteriors, lithium secondary batteries may be classified into can-type secondary batteries, in which an electrode assembly is embedded in a metal can, and pouch-type secondary batteries, in which an electrode assembly is embedded in a pouch of an aluminum laminate sheet.
Recently, secondary batteries are widely used in medium and large-sized devices such as automobiles or power storage devices as well as in small-sized devices such as portable electronic devices. When secondary batteries are used in medium and large-sized devices, a large number of secondary batteries are electrically connected to each other for improving capacity and output. In particular, pouch-type secondary batteries are frequently used in medium and large-sized devices due to a merit of being easily accommodated and stacked.
FIG. 1 is a schematic diagram illustrating a battery module according to the related art.
As such, a battery module 1 may refer to a component in which a large number of secondary batteries 22 are connected in series or parallel for improving capacity, output, and the like. Generally, the battery module 1 includes a case 10 accommodating a secondary battery stacked body 20 in which the large number of secondary batteries 22 are stacked. In addition, as shown in FIG. 1, the case 10 includes an upper case 12 accommodating an upper portion of the secondary battery stacked body 20 and a lower case 14 accommodating a lower portion of the secondary battery stacked body 20, and the upper case 12 and the lower case 14 are fastened to each other by a bolt 30. As shown in FIG. 1, the bolt 30 is mounted such that a screw portion 32 is inserted into a bolt hole 16 pierced in the upper case 12 and screw-coupled to the lower case 14, and that a bolt head 34 is caught by the upper case 12, thereby fastening the upper case 12 and the lower case to each other.
However, when internal gas is generated from the secondary batteries 22 during charge-discharge of the secondary batteries 22, there is a concern that the internal gas of the secondary batteries 22 is leaked outside the battery module 1 through the bolt hole 16 of the upper case 12. To solve this problem, in the battery module 1 according to the related art, an O-ring 40 is mounted to be interposed between the bolt head 34 and the upper case 12, thereby sealing the bolt hole 16. The O-ring 40 is mounted for the screw portion 32 of the bolt 30 to be inserted into a hollow thereof, and thus is interposed between the bolt head 34 and the upper case 12. However, since the O-ring 40 generally has a smaller diameter than the bolt head 34, the bolt 30 needs to be separated from the bolt hole 16 for inspecting whether the O-ring 40 is mounted. Therefore, in the battery module 1 according to the related art, there are problems in that a lot of time is required for inspecting whether the O-ring 40 for sealing the bolt hole 16 is mounted, and that there is a concern of occurrence of errors in inspection results due to a complicated method of inspecting whether the O-ring 40 is mounted.
In addition, since the O-ring 40 is generally manufactured from a synthetic material having elasticity, there are some cases in which the O-ring 40 is twisted to be dragged toward the center thereof due to a shear force applied between the bolt head 34 and the O-ring 40 in the process of tightening the bolt 30. As such, when the O-ring 40 is twisted, the internal gas of the secondary batteries 22 may be leaked outside the battery module 1 through the bolt hole 16, like in the case that the O-ring 40 is not mounted. To inspect the twist of the O-ring 40, the bolt 30 needs to be separated from the bolt hole 16, like in the case of inspecting whether the O-ring 40 is mounted. Therefore, in the battery module 1 according to the related art, there are problems in that a lot of time is required for inspecting whether the O-ring 40 for sealing the bolt hole 16 is twisted, and that there is a concern of occurrence of errors in inspection results due to a complicated method of inspecting whether the O-ring 40 is twisted.